The United Nations general assembly has seldom over the past half century faced so many crises in a single week. Leaders and foreign ministers from 192 countries are confronted with: the potential civil war in Iraq, policing the ceasefire in Lebanon, the Darfur catastrophe, Iran's alleged nuclear programme and, as with past years, the Israeli-Palestinian conflict.

At the end of the week it is unlikely if any of these or the many other conflicts and problems being discussed in the chambers, offices and corridors of the UN will be resolved, and renewed questions will be asked about the relevance of the world organisation.

The biggest critics remain the US neo-conservatives, reflecting American rightwing suspicion of the UN since its founding. They see the UN as anti-American, anti-Israel, defending totalitarian governments, squandering billions, bureaucratic, ineffective.

Debilitate

One of the critics, Joshua Muravchik, resident scholar at the neo-cons' favourite thinktank, the American Enterprise Institute, and author last year of The Future of the United Nations, said yesterday: "The UN has been an enormous failure. It is true it has done a small number of things usefully, including peacekeeping missions. My question to those who say that it is better to have it than not is that when peacekeeping missions have been organised under the auspices of other bodies (such as Nato), I am not sure if the UN brings any value."

Supporters of the UN respond that US ambivalence about the organisation, and often outright hostility, debilitate it. They point to the list of successes since its founding after the second world war and contrast these with the dismal record of its predecessor, the League of Nations, and the rapid rise over the past 10 years in peacekeeping missions.

They concede that it is an imperfect organisation, where resolutions are passed and ignored, money wasted and conflicts go unresolved, but argue, as Mr Muravchik anticipated, that the world is still a better place with it than without.

The UN has a polarising effect, with supporters and opponents dividing as true believers or sceptics. One of the UN supporters, Lord Hannay, the British ambassador to the organisation between 1990 and 1995, while acknowledging that this was how the debate is often conducted, said it was the wrong way to view the organisation. He argues that a more hard-headed approach should be taken, acknowledging the UN's strengths and weaknesses.

"Can the world get on without it? The answer is no," said Lord Hannay, who remains engaged with the UN as a member of the high panel set up by the secretary general, Kofi Annan, to look at the organisation's reform. "Is it doing all it can do? The answer is no. The question is how can we make it better and doing the things we want it to do.

"The lessons of the last few weeks are its indispensability and its ineffectiveness." He saw, as the example of its indispensability, the putting together of a ceasefire and peacekeeping force for Lebanon and, of its ineffectiveness, the failure of the UN so far to persuade the Khartoum government to allow a peacekeeping force into Darfur.

In the first 35 years of its history the UN was largely constrained by the cold war. Since 1991, when that ended, it has faced an increasing number of conflicts. Within the space of 18 months between 1993 and 1995 it had to deal with Somalia, Bosnia and Rwanda; its performance was abysmal. Its biggest test after that was Iraq in 2003, which demonstrated the inadequacy of the UN in the face of US determination to go to war. And now the many problems of this week.

Although few, if any, would predict significant progress on the Israel-Palestine conflict by Friday, the general assembly showed its value as a forum when the Palestinian president, Mahmoud Abbas, yesterday met the Israeli foreign minister, Tzipi Livni, for 90 minutes. There will be many such meetings on other issues in the UN building this week.

Mr Muravchik regards this as one of the UN's few strengths. "Some people criticise it for being a talking shop. I think it should be a talk shop. It is useful that all the governments should come together. This is a healthy and valuable function." The problems began, he said, when it came to voting and taking action. His preference for the UN would be as "a glorified Hyde Park Corner".

He described Mr Annan, whose 10 years in office end on December 31, as "having such a wonderful presence and [being] very seductive" but having failed. "I think ill of him. The last secretary general I think well of is Dag Hammerskjold [the Swede who was the second person to hold the post]."

The UN security council is in the process of selecting Mr Annan's successor but the list of candidates so far is unimpressive.

Protection

The general assembly last year agreed to some reforms - accepting a duty to protect people from their own abusive governments, the creation of a human rights council to replace the discredited human rights commission and the creation of a new peace-building commission - but rejected others.

Darfur shows the weakness of the UN, acknowledging a duty of protection but unable to implement it. Lord Hannay said: "The UN has not been able to stop what is happening [the slaughter in Darfur] but it may have been able to slow it down."